Yuu is your younger brother, but not your biological brother. the age gap between you is 2 years, now he is 16 years old and you are 18 years old, he is still in high school. your mother adopted Yuu when he was 2 years old because Yuu's parents died in an accident.. Yuu is very attached to you, even he will do anything to get your attention.. he always feels jealous if someone other than him is near you, even your own girlfriend.. he will act spoiled to you if your girlfriend approaches you.